Dosing device for the volumetric dosing of a liquid additive

Abstract

A dosing device for volumetric dosing of a liquid additive which is added in a certain volume ratio to a fluid, in particular withdrawn blood, flowing in a first hose line, via a second hose line feeding directly or indirectly into the first hose line. The dosing device for the volumetric dosing of an anticoagulant fluid or a sedimentation accelerator is preferably provided in a system for the collection and retransfusion of autologous blood which has a hose or tube section which extends downstream from the junction, and also a drip chamber connecting downstream from the drip tube and a light barrier, the direction of action of which is arranged transversely to the fall path of the drops. In order to avoid incorrect dosing because of changing viscosities of the liquid flowing in the first hose line, and thus of changing drop sizes, two electrically-triggerable valve means, one of which is in each case inserted into one of the two hose lines, are provided. The valve means are triggered alternately by means of a counting and control unit in such a way that in each case only one of the two named hoses is switched to "open" at the same time. The liquid remaining in the drip tube as a result of capillary action thereby brings about a volume constancy between drops falling at the lower end of the drip tube and additive which is added at the upper end of the drip tube.

What is claimed is: 
     
       1. A dosing device for volumetric dosing of a liquid additive which is added in a certain volume ratio to a fluid flowing in two hose lines comprising a first hose line and a second hose line which feeds directly or indirectly into the first hose line, said dosing device comprising two electrically triggerable valve means which are each inserted into one of two hose lines and coupled so that only one of the two valve means is switched in a switching cycle to an open position; a counting and control unit (CPU, RAM); a drip tube which extends downstream from a junction; a drip chamber connecting downstream from the drip tube; and a light barrier, the direction of action of which is arranged transversely to a fall path of drops of additive, whereby drops falling in the drip chamber are counted and the valve means is alternately triggered by the counting and control unit after a certain number of drops have been counted. 
     
     
       2. A dosing device according to claim 1, wherein the two valve means comprise a 4/2-way valve. 
     
     
       3. A dosing device according to claim 1, wherein the two valve means comprise a 3/2-way valve. 
     
     
       4. A dosing device according to claim 2 wherein the 4/2-way valve is spring-loaded, and the first hose line is switched to the open position in a resting position. 
     
     
       5. A dosing device according to claim 1, wherein the valve means comprise a 3/3-way valve which has a spring-centered middle position in which the two hose lines are blocked. 
     
     
       6. A dosing device according to claim 1, wherein the counting and control unit comprises a freely programmable memory (RAM), inputting means for entering a value (N) representing a number of drops, and a central processing unit (CPU) for generating a control pulse for alternate triggering of the valve means when an ascertained number of the drops reaches the value (N) stored in the freely programmable memory (RAM). 
     
     
       7. A dosing device according to claim 1, wherein the counting and control unit comprises a freely programmable memory (RAM) in which there is provided a memory space for a constant (A) which corresponds to the number of drops of additive to be added per switching cycle of the valve means. 
     
     
       8. A dosing device according to claim 1, wherein the counting and control unit comprises a central processing unit (CPU) and a freely programmable memory (RAM) in which an operating program for the processing unit is stored which controls the valve means alternately so that after a certain number of switching cycles of the valve means, a switching cycle is carried out in which the second hose line conveying the additive is switched through until the volume of additive which has flowed out, as determined by the light barrier, corresponds substantially to the volume of the drip tube and any dead spaces in the valve means. 
     
     
       9. A dosing device according to claim 1, wherein the two hose lines, the two valve means, the drip tube, and the drip chamber comprise disposable parts. 
     
     
       10. A dosing device according to claim 9, wherein the drip chamber and the light barrier are constructed such that the drip chamber constructed as a disposable part can be locked in the correspondingly constructed light barrier. 
     
     
       11. A dosing device according to claim 10, wherein the drip chamber is lockable in a form-locking manner with a component comprising the light barrier.